In backlight computer displays or other display systems, optical films are commonly used to direct light. For example, in backlight displays, light management films use prismatic structures (often referred to as microstructure) to direct light along a viewing axis (i.e., an axis substantially normal to the display). Directing the light enhances the brightness of the display viewed by a user and allows the system to consume less power in creating a desired level of on-axis illumination. Films for turning or directing light can also be used in a wide range of other optical designs, such as for projection displays, traffic signals, and illuminated signs.
Materials suitable to form light management films desirably have particular physical and mechanical properties. The material should be easy to process to form the necessary microstructure to turn or direct light. The material should have a high index of refraction. Materials with high index of refraction provide light management films having better brightness than corresponding material having a lower index of refraction. Desirably the material has a glass transition temperature high enough to withstand the rigors of the particular application without deformation. Finally, the film material should provide minimal scattering or absorption of light
Current materials for light management films include composites made from a combination of a curable material and a flat film substrate. The microstructure is contained in the cured portion of the composite, which is made by charging curable material to a structured mold followed by curing. The substrate film generally used is polyethyleneterephthalate (PET) or polycarbonate, which can be disposed on the curable material prior to the curing step. This combination results in the use of at least two materials and requires a number of steps to prepare the final structured film composite.
While a variety of materials are presently available for use in light management films, there remains a continuing need for still further improvement in the materials used to fabricate them, particularly materials that possess the combined attributes desired to satisfy the increasingly exacting requirements for light management film applications while at the same time resulting in a reduction in the number of materials and ease of production.